Rotary impact tools are one of the most efficient means of mechanization employed in carrying out assembly and mounting operations. The principle of operation of such a tool is based on conversion of a drive motor continuous rotation into repetitive impulses (impacts) delivered by a high-mass rotary part (hammer member) to the output shaft (spindle) of the tool.
Due to the fact that the time of accumulation of kinetic energy by the hammer member is much greater than the time of collision (the time of transmission of the energy accumulated by the hammer member to the spindle), the force developed by the spindle is from 400 to 500 times greater than that on the shaft of the drive motor. This makes it possible to create high-power compact tools of a low mass. Another important advantage of rotary impact tools lies in the absence of a reaction torque transmitted to the hands of an operator.
Known in the prior art is a rotary impact tool (Cf. U.S. Pat. No. 2,718,803, U.S. Cl. 81-523) comprising a case enclosing a drive motor transmitting rotation through an intermediate member to a hammer member embracing a spindle. The spindle is coaxial with the intermediate member. It bears with its one end on the intermediate member and with its other end on the case. The spindle is provided with longitudinal projections made on its outer surface. These projections interact with corresponding projections on the inner surface of the hammer member. The hammer member is mounted to reciprocate along guide means in a plane perpendicular to the axis of rotation. The intermediate member transmitting rotation to the hammer member is mounted directly on the shaft of the drive motor and has a fork-like driver engaging with the projection on one of the end faces of the hammer member and transmitting rotation thereto through this projection. Translation of the hammer member in a plane perpendicular to the axis of rotation in this construction is provided by a pivot with the hammer member mounted to swing thereon. This pivot is fixed in a holder embracing the hammer member. As the hammer member rotates, the impact projections on the inner surface of the hammer member repeatedly, that is at every revolution, engage with (deliver impacts to) the longitudinal projections on the spindle outer surface. Swinging of the hammer member about the pivot (hammer member translation) provides disengagement of the hammer member projections from the spindle projections after collision and a required orientation of the hammer member projections relative to the spindle projections in the course of rotation.
However, it may be seen from the above that in this prior art construction the hammer member translation is provided by a group of component parts (the intermediate member, holder, pivot), and this appreciably complicates the construction.
Besides, the fork-like driver of the intermediate member transmitting rotation to the hammer member engages the end projection of the hammer member along a line, and thus the collision between the hammer member and the spindle along this line causes high contact stresses resulting in the formation of dents in the surface of the fork-like driver, hammer member jamming, and tool failure.
The reliability of the tool is also affected by the fact that one of the spindle supports is not rigid (the spindle bears against the shaft of the drive motor through the intermediate member). This, firstly, results in a rapid wear of the spindle and hammer member projections on colliding and, secondly, develops an additional dynamic load on the motor shaft.
Also known in the prior art is a rotary impact tool (Cf. U.S. Pat. No. 3,072,232, U.S. Cl. 173-93.5) whose construction is the nearest prototype to the proposed construction. The tool has the same construction of an intermediate member and of the projections on a hammer member and spindle as the analog considered hereinabove. Rotation from a motor to the hammer member is also transmitted through a fork-like driver of the intermediate member and the end projection on the hammer member.
The main difference between this tool and the analog considered hereinabove consists in that the holder accomodating the hammer member is provided with a hole of a rectangular shape. The hammer member is also rectangular in its longitudinal section and mounted to move along the hole in the holder, i.e. the hole in the holder serves as a guide means to provide hammer member motion in a plane perpendicular to the axis of rotation.
Such a construction of the tool is simpler and more reliable than that considered hereinabove.
However, to provide hammer member translation, this construction also utilizes a number of component parts.
Besides, the fork-like driver of the intermediate member engages the end projection of the hammer member in the same way along a line, which causes appreciable contact stresses resulting in rapid wear and failure of the tool.
One of the spindle ends in this construction, as in the aforementioned one, also bears through the intermediate member on the drive motor shaft which takes dynamic loads as the hammer member delivers impacts to the spindle, and that also affects the tool reliability.